London has been battered by 50mph winds that have felled trees and caused travel chaos. Powerful gusts swept across the capital as the Met Office issued a yellow "be aware" weather alert for most of the country.

If anybody can justify a bout of the back-to-work jitters today, it is Dave Lewis. Not only does the long-serving Unilever director become the first outsider to take over the reins of Tesco, Britain’s biggest retailer, but he is being drafted in a month earlier than planned.

Last Friday’s second profits warning in six weeks, which was combined with the dividend being slashed and spending culled, confirmed that Tesco’s crisis is deepening. Lewis is being painted as the superhero to save an institution that has badly lost its way.

It would be easy to be overwhelmed by the pressure. But as he sweeps into a meeting room at Unilever’s art deco headquarters on the Embankment, Lewis is clearly buzzing with it. Tanned and wiry, with hair chopped short, greying at the sides, he is dressed in trendy dark jeans, chunky watch, white shirt with several buttons undone, carrying a cup of coffee and Moleskine notebook. Immediately, here is a break from the staid, buttoned-up Tesco era of predecessor Phil Clarke, even if, at 49, Lewis is only five years his junior.

“How can I help you?” he shoots across the table, pleasantries aside. No wonder Lewis has a reputation for putting the customer first. He is slick, but later comes a confession.

“I am wonderfully naïve about some of the stuff that is going to come but that is fine, it has served me well up to now,” he says, vowels flat from his Yorkshire upbringing. “I will do what I have to do tomorrow in the same way that I did things yesterday.”

Tesco has swapped one company lifer for another. Clarke, who began work 40 years ago as a schoolboy in the store his father managed, is being succeeded by Lewis, who planned to leave Unilever after two years to run his own business but instead has jetsetted through postings in South America, Indonesia and back to Britain in a 27-year career. The debate rages over whether the one-time marketer, who sold Dove soap and TRESemmé shampoo by the bucket load, is the right man to stop the rot. For his part, he couldn’t resist answering the call.

“I needed to find out for myself whether I can lead a whole business,” Lewis says. “Some people think that is crazy given some of the jobs I have done but actually I don’t think you know whether you can truly lead a business until you sit in that seat.”

He admits that “the bit that is interesting is that I have never run a shop in my life”, pointing out that a lot of the other parts of retail, such as category management and logistics, are very similar at Unilever. Besides: “Phil Clarke is a great retailer. The issue for Tesco is, is that what they need now? Because great retailing in that seat hasn’t been the thing that has worked, so they do need a fresh perspective.”

He may be fiercely ambitious, but the divorcee’s two daughters, aged 18 and 15, keep him grounded.

“I had to tell them on the Sunday (the day before he was revealed as Tesco’s new leader). They were like, ‘Dad, what are you talking about?’ I never talk about work with them really. They were both somewhat shocked by what happened.”

In the days that followed, Lewis’s mobile phone went into meltdown. One text message sticks in his mind from his youngest. It read, “Fitness fanatic? Who are you kidding?”, referring to his reported running obsession that began when he agreed to take part in the (Unilever-owned) Flora London marathon.

For the record, Lewis does love running, but also cooking, photography and “I play golf, I play any racket sports.” Living in Richmond, “it is the river, it is the park, it is just trying to keep fit”.

But the biggest misconception that Lewis wants to correct is that he is purely a marketer. Yes, he did launch Dove soap in Britain in 1992, but no, he didn’t create Dove’s Real Beauty campaign for which he keeps getting credited. And he has done a lot since then, not least expanding sales at Unilever’s £16 billion-a-year personal care division — think Lynx deodorant, Radox, Brylcreem and Vaseline — by more than a third.

“In personal care, we won something like 50 Lion awards at the Cannes advertising festival. I’ve never been to Cannes; I have no desire to go to Cannes. They did the work, I just created the environment and the stimulus.”

He is more relaxed about his “Drastic Dave” nickname, coined in the trade press when he was drafted back in to the UK division to arrest a sales slump with a brutal restructuring and a table-thumping mantra of “we win because we care”.

“It wasn’t an easy situation, it wasn’t a time for incremental improvements. We needed to make some significant changes.” With profit margins under pressure from cut-price upstarts Aldi and Lidl, Tesco folk beware. The retailer is reeling after calling an end to the “space race” of store openings, retrenching overseas and Clarke’s detours into posh coffee shops and launching its own tablet computer.

Lewis adds: “I do genuinely think that leaders don’t have just one style. I know everybody wants to profile and pigeonhole but the job of a leader is can you adapt to a situation you find yourself in? OK, Drastic Dave makes you sound like you are some sort of hatchet man who turns around businesses in a very particular way, but you go forward and take the personal care example, which is what does the task need at the time?”

For the past three years, Dashing Dave might be more appropriate. He moved quickly to expand a business he won’t describe as beauty because he is adamant his clientele are beautiful already. Listen to him sitting down with a group of Dove shoppers.

“When you talk to those women you say, ‘OK, tell me about what you do on Friday night, when you have done all the parental things’. They will tell you about an aspiration to walk into a room and for it to go quiet. To have a partner who occasionally looks at them with desire and lust in their eyes.”

One big achievement, the segmenting of the shampoo market, is interesting given that Tesco must overhaul its ranges after learning the hard way that the one-size-fits-all era is over.

Unilever did best at the lower end of the market but Lewis wanted more premium brands too. It bought some, such as TRESemmé and Toni & Guy, which also brought with it a hair academy in Battersea whose stylists can provide instant feedback on new innovations.

“It is about providing inspiration and insight into the market. I suspect that your wife’s conversation with her hair stylist has a content unlike any other,” he surmises.

Lewis also let the science boffins loose, such as by bringing a version of TRESemmé with salon-style keratin treatment to the supermarket shelves. Knowing what customers want is what unites it all, a trick that has in recent years deserted Tesco.

“One of the things I have loved from the favelas in Brazil to the islands of Java is getting that connection with consumers. The one thing I said to people who join Unilever is ‘I don’t care what function you are in, if you are not curious about people, don’t join’.”

It is a curiosity that has led him all the way up Tesco’s troubled aisles. Now can Driven Dave unite checkout girls and disillusioned directors to put the super back into Britain’s biggest supermarket?